An electroconductive roll used for a charge roll of an electrophotographic copying machine is required to have an electroresistivity in the range about from 10.sup.3 to 10.sup.9 .OMEGA. (hereinafter roll resistance means a determined value using an electrode having an area of 1 cm.sup.2) and is usually composed of a metal shaft and an electroconductive layer formed on the outer surface of the shaft.
Such kind of electroconductive roll is considered to have preferably an electric resistance level in the range from 10.sup.3 to 10.sup.9 .OMEGA. as described above In order to fulfill a sufficient function as a charge roll. The charge roll is required to have an elasticity since the roll is rotated in pressure-contact with the outer surface of a photo-sensitive drum and the outer surface of the photo-sensitive drum is charged with the rubbing friction at the contact area. Thus the above electroconductive layer is generally formed from an electroconductive rubber composition prepared by mixing electroconductive powders or electroconductive fibers (e.g. carbon black, metal powders, metal oxides, carbon fibers) in a synthetic rubber such as silicone rubber (Japanese Patent Unexamined Publication No.Sho-58-49960 and Japanese Utility Model Unexamined Publication No. Sho-58-88645). in addition, a charge roll having an ionic electrophotographic elastic layer which is prepared by using an ionic electroconductivity of a synthetic rubber itself or by adding a high dielectric solution or an ionic material to the synthetic rubber so as to reinforce the ionic conductivity of the above synthetic rubber is also known (Japanese Patent Unexamined Publications No. Hei-1-277257 and No.Hei-2-198470). However, if charging is repeated in a state that the electroconductive rubber layer and the photoreceptor surface are in direct contact with each other, there exist a problem that a low molecular component contained in the rubber layer will migrate into the photoreceptor to cause image defects. Further there exist a problem that the rubber layer will wear out by contacting with the photoreceptor and the roughness of the roll surface is changed largely from the initial state and the uniformity of the charging is deteriorated. Further, when the electroconductivity of the electroconductive rubber layer is high, so called pinhole leak where excessive electrical current flows in defect area of the photoreceptor will occur and image defects will appear.
In order to solve such problems, a resin layer comprising a resin having a lower resistance is formed on The surface of an electroconductive rubber layer as a protective layer (Japanese Patent Unexamined Publications No. Sho-58-194061 and No. Sho-64-66674). However, in the case, resistance values and image concentrations are varied depending on atmospheric conditions. Thus an attempt to add an electroconductive material such as carbon black to the surface resin layer is made but it has a problem that a dielectric breakdown of an photoreceptor or charge roll can not be inhibited depending on the type of the defects of the photoreceptor. Therefore, an attempt to add an electroconductive particles having an electric resistance of 10.sup.1 to 10.sup.5 .OMEGA.cm to a resin (Japanese Patent Unexamined Publication No.Sho-64-66675). However, the dielectric breakdown can not be inhibited by the attempt, there still exist problems.
As explained above, the conventional charge rolls have problems such as photoreceptor contamination, pinhole leak, atmospheric change of resistance value or deteriorations due to attachment of foreign materials or wear and thus a satisfiable roll has not obtained.